Over the holidays I also finished the 8.1 Horde War Campaign. Like the Alliance version, there were three chapters, and the last chapter waits for the raid to open. There's also a second questline involving Saurfang.
The first chapter is a raid on the Norwington Estate to destroy stockpiled azerite weapons. It featured Rexxar. It was pretty straightforward as these things go.
The second chapter was a goblin escape with Gallywix and a mech. This was okay, if you're a fan of goblins you'd probably like it. I'm not, so I wasn't particularly enthused. There are some funny lines here and there.
The third chapter involved springing Lady Ashvane from Tol Dagor. Your compatriots are Rexxar and Arcanist Valtrois of the Nightbourne. I really like how Blizzard is reusing Allied Race NPCs in this expansion. I like Valtrois, and it's good to see her return. The actual quest is an enjoyable prison-break, featuring disguises and explosions.
The other major quest is the Saurfang quest. This is an excellent quest, as you try to discover what happened to Saurfang as he escaped Stormwind. It's really worth having a Horde character to go through it.
You even get to make a choice at the end to side with Saurfang or Sylvanas. Which is great, except it points up one of the downsides of this thing. I sided with Sylvanas on my blood elf, so to see the other side, I'd need yet another Horde character. I'm debating leveling an Allied Race, or simply using my BfA boost on a Horde character. I don't think the choice will make much difference in the long run, though.
In any case, the Horde War Campaign was a good counterpart to the Alliance one. The story is beginning to heat up, so we'll see what happens when the raid opens in a couple of weeks.